Applicability of the MIRI repeatability systematic uncertainty

Determine to what extent the $\sigma(\rm repeat)=0.45\%$ systematic error term for JWST MIRI photometry should be applied when analyzing multi-epoch TRAPPIST-1 observations.

Background

The analysis compares stellar fluxes across multiple JWST visits, making the treatment of repeatability-related systematic errors important. The paper explains that the σ(repeat)\sigma(\rm repeat) term could arise either from visit-dependent persistence effects, in which case it might not apply, or from point-spread-function variations caused by changes in the phasing of JWST mirror segments, in which case it would apply. The physical origin of this uncertainty is unresolved, and the authors therefore omit the term optimistically for their demonstrative analysis.

References

However, it is unclear to what extent the $\sigma(\rm repeat) = 0.45\%$ systematic error term from should be applied for our treatment of these data. On one hand, because our observations are all time-series observations and the mid-eclipse time for each visit is well after the start of the observations, they will be less affected by different levels of persistence from whatever MIRI filter was previously in-place and whatever field MIRI happened to be pointed towards (since MIRI doesn't use a shutter and is exposed to the sky at all times), and the $\sigma(\rm repeat)$ term may not apply to our situation. On the other hand, the $\sigma(\rm repeat)$ systematic error term from may instead be dominated by variations in the PSF due to changes in the phasing of each of the different mirror segments between different visits, in which case $\sigma(\rm repeat)$ would equally apply to our analyses. Ultimately, the answer is unclear and further study into the cause of this systematic uncertainty is needed, so we optimistically chose to ignore the $\sigma(\rm repeat)$ term for our demonstrative paper.

Looking for TRAPPIST-1 external planets' emission in JWST archival data  (2608.18626 - Cartigny et al., 19 Aug 2026) in Section 2.2.1, Calibrated stellar flux